The present invention relates generally to a tristimulus colorimeter and, more particularly, to such a colorimeter that is adapted for measuring the color of teeth. Moreover, the invention relates to improvements in such a colorimeter with these improvements also being useful in other types of systems, such as, for example, those having optical or non-optical transducers for detecting particular phenomena and measuring circuitry that measures the electrical output of the transducer to provide a visual display and/or a control function.
Although the invention will be described with reference particularly to a reflection type tristimulus colorimeter that produces a digital display indicative of the red, green and blue color components of a tooth, it will be appreciated that the various features of the invention may be employed with other types of color or non-color reflection or transmission types of optical measuring systems, non-optical transducer input measuring systems, and the like.
Related U.S. patent applications which include subject matter pertinent to the invention of this application and are commonly assigned are as follows: Ser. No. 499,479, filed Aug. 22, 1974, now U.S. Pat. No. 3,986,777; Ser. No. 696,787, filed June 16, 1976, now U.S. Pat. No. 4,055,813; Ser. No. 698,143, filed June 21, 1976, now U.S. Pat. No. 4,080,074; and Ser. No. 721,107 filed concurrently herewith for "Comparison Type Colorimeter."
In the first application a colorimeter is disclosed employing a multiplexed dual slope integrator type of digital voltmeter to provide a digital display of red, green and blue components of light reflected from an object. In the dual slope integrator a first electrical signal derived from a photosensor is compared with a reference electrical signal from an electric energy source, and the visual display of digital color values is related to the results of that comparison. A color filter wheel cyclically sequentially interposes red, green and blue filters in the unknown light beam reflected by the object to the photosensor, and the multiplexing circuitry is synchronized to the wheel and is reset on each complete cycle. The synchronized multiplexing circuit then automatically controls operation of the dual slope integrator to place respective calibrating circuits therein and to deliver electrical output signals therefrom to respective red, blue and green visual displays.
In the second and third applications there are respectively disclosed a "Single Adjustment Multiple Function Calibration Circuit" to facilitate compensation for drift in a multiplexed amplifier having plural feedback channels selectively coupled thereto and an "Automatic Zeroing Circuit To Compensate For Dark Currents or the Like" to eliminate inaccuracies in measurements due to commonly experienced dark current or other leakage current in the transducer.
In the last application an arrangement of the optical elements, including light pipes and color filters for illuminating an object and for sequentially directing unknown beams of colored light reflected from the object and reference beams of corresponding colors to a common photosensor, is disclosed. This as well as other optical measuring and testing devices may experience optical error, whereby a known portion of incident, reflected or other light passing through one or more optical elements of the system is diverted, for example, by reflection from one to another of plural light paths or is simply attenuated by the optical elements. Since such optical error is usually due to internal reflection, for example, within a bifurcated light pipe or other optical elements through which two or more light beams simultaneously pass, such optical error will be referred to hereinafter as reflectance error; however, it will be understood that reflectance error also means other types of optical error as well.